A batch kneader is a kneader for producing one batch worth of kneaded materials by performing a series of operations including the steps of kneading polymeric materials (materials to be kneaded) such as rubber and plastic which are placed in a kneading chamber through a hopper unit and sealed inside such kneading chamber at a prescribed pressure using a pair of kneading rotors provided in the kneading chamber, and thereafter externally discharging the kneaded materials in an intended kneaded state. Here, among the parts configuring the batch kneader, the kneading rotor is a key part for kneading the materials to be kneaded. Conventionally, for instance, the following types of technologies concerning a kneading rotor have been proposed.
Applicant has previously proposed a kneading rotor comprising a nonlinear blade in which the developed shape from the starting point to the ending point becomes nonlinear when developed in a planar state around an axis (for instance, refer to Patent Document 1). The kneading rotor described in Patent Document 1 is a four-blade rotor comprising a total of four blades; specifically, two long blades and two short blades. One blade among the four blades of this kneading rotor is the foregoing nonlinear blade (long blade), and the remaining three blades are linear blades in which the developed shape thereof becomes linear. With the kneading rotor described in Patent Document 1, the mixing and dispersion of the materials to be kneaded can be balanced efficiently as a result of the existence of the nonlinear blade and, consequently, kneading can be appropriately controlled so that the mixing of the materials to be kneaded and the dispersion of prescribed materials in the materials to be kneaded can be performed concurrently.
In addition, a different applicant proposed a kneading rotor comprising a total of four blades; specifically, two long blades which are both linear blades having different twist angle and two short blades which are both linear blades having different twist angle (for instance, refer to Patent Document 2). According to the kneading rotor of Patent Document 2, the materials to be kneaded can be subject to favorable distributive and dispersive mixing and, consequently, the discharge temperature of the kneaded materials can be controlled to be a lower temperature, and it is possible to obtain a more homogeneous kneaded material.
Nevertheless, if the kneading rotor described in Patent Document 1 is used to knead materials to be kneaded to which, for example, large amounts of silica are added (compounded) thereto, the ΔG′ value as the dispersion index of silica did not become a favorable value. Here, the ΔG′ value is, among the storage elastic modulus obtained from the viscoelastic property of the unvulcanized rubber composition, the difference between the value at the time the rubber composition generated small strain and the value at the time the rubber composition generated large strain, and is an index that is used for determining the quality of the kneaded materials. The smaller the ΔG′ value, the better the quality of the kneaded materials. When kneading the materials to be kneaded which are compounded with silica, the silane coupling agent that is compounded for bonding silica and rubber will react with silica when the temperature of the kneaded materials is in a range of, for example, 140° C. to 160° C. Therefore, in order to cause a favorable reaction, it is necessary to sufficiently and evenly knead silica and the silane coupling agent in a temperature range of approximately 140° C. to 160° C. Kneading that is performed in a temperature range of approximately 140° C. to 160° C. corresponds to kneading of a rubber-based composition in a high temperature state.
The key feature of the kneading rotor described in Patent Document 2 is that the twist angle of the two long blades is mutually different. Nevertheless, even with the kneading rotor comprising the nonlinear blade described in Patent Document 1, the twist angle in most parts of the two long blades is mutually different. Specifically, the kneading rotor described in Patent Document 2 is similar to the kneading rotor described in Patent Document 1 in terms of the configuration and arrangement of the blades. Thus, even if the kneading rotor described in Patent Document 2 is used, it can hardly be said that favorable kneaded materials can be obtained as a result of kneading the materials to be kneaded, to which large amounts of silica have been added, in a high temperature state.
Patent Document 1: Japanese Patent No. 3980841
Patent Document 2: Japanese Unexamined Patent Application No. 2004-530546